A partitioned dynamic ammonia injection strategy based on real-time NOx flux distribution characteristics in an SCR system

Abstract

To optimize the NO_x/NH₃ (Nitrogen Oxides/Ammonia) matching ratio for a SCR (Selective Catalytic Reduction) system, dynamic NH₃ injection was achieved on the basis of the constructed control rules for critical AIG (Ammonia Injection Grid) branch-pipe valves via the determination of the basic NH₃ injection amount and the secondarily distributed NH₃ injection amount. Moreover, the real-time NO_x flux distribution characteristics in each subzone were analysed on the basis of the operation data of the flue gas velocity and NO_x concentration originating from multiple measuring points located in the flue cross-section which is in front of the AIG. The engineering application results of a 350 MW coal-fired unit revealed that 12 “critical” AIG branch-pipe valves achieved dynamic NH₃ injection. With a maximum fluctuation in NO_x flux of 433 mol/h in the subzone of the individual flue cross-section, the opening of this AIG branch-pipe valve was subsequently adjusted by 22° to optimize the NO_x/NH₃ matching ratio in the system in a timely manner. The ACRs (Ammonia Consumption Rates) of the A and B sides in the studied SCR system were reduced by approximately 26.70 % and 11.90 %, respectively. In addition, the average RSD (Relative Standard Deviation) of the NO_x concentration at the outlet of the SCR reactor for sides A and B were approximately 11.9 % and 13.6 %, which were reduced by approximately 11.63 % and 15.47 %, respectively, owing to the application of the dynamic NH₃ injection strategy.